Blocking ion diffusion and minimizing electron charging in solid electrolytes under electron-beam irradiation for transmission electron microscopy analysis

Evaluating ion-conductive solid electrolytes (SEs) accurately is crucial for advancing solid-state battery technology. Scanning/transmission electron microscopy (S/TEM) is a valuable technique for examining the local characteristics of battery materials. However, the tolerance of SEs to high-energy electron beams is notably lower than that of electrode active materials, because SEs generally have low electron conductivity. Here, we propose a specialized coating technique for TEM samples, termed “nano-shield,” which enables stable and accurate observation of their micro-/nano-structures. Nano-shield consists of a dual-layer coating combining an amorphous insulating layer of aluminum oxide (AlO_x) with a conductive carbon (C) film. The AlO_x layer blocks ion diffusion in the TEM samples, and the C layer minimizes electron charging during electron-beam irradiation. By applying a nano-shield, we successfully visualized the atomic structures of a lithium-ion-conductive SE, Li_1.3Al_0.3T_1.7(PO₄)₃ (LATP), by using STEM at room temperature. Additionally, we performed a precise elemental analysis of a sodium-ion-conductive SE, Na₃Zr₂Si₂PO₁₂ (NZSP), via STEM equipped with energy-dispersive X-ray spectroscopy (STEM-EDS). Our findings demonstrate that nano-shield enhances the reliability of S/TEM observations of SEs and sheds light on its underlying protective mechanisms.